1. Field of the Invention
The present invention is generally related to a method for detecting the occurrence of engine knock events and, more particularly, to a strategy which achieves the advantages of a moving average technique without the inherent disadvantages of requiring significant memory for storing data and time for data manipulations and calculations.
2. Description of the Prior Art
Improper combustion, which is commonly referred to as knock, is a well known limitation on internal combustion engine power generation. To achieve maximum engine power, it is necessary to appreciate the disadvantages of engine knock and provide an efficient method for detecting it.
When an additional flame front is initiated at the cylinder walls due to the increasing temperature and pressure resulting from the spark initiated flame front, engine knock will occur. When these two flame fronts collide with each other within the combustion chamber, cylinder pressure spikes and resonates causing piston and valve pitting, and crankshaft and rod bearing degradation. Engine knock dramatically decreases the life of an internal combustion engine and appropriate actions must be taken in order to limit this phenomena.
The various causes and cures of engine knock are generally known to those skilled in the art and will not be described in detail herein. In addition, various methods for measuring and monitoring engine knock are also well known. Basically, a pressure transducer can monitor the pressure waves within the combustion chamber and provide signals that represent the variations in intensity sensed by the pressure sensor. An accelerometer can be used to detect forces that cause vibration of the engine. Accelerometers provide signals that represent the intensity of the vibrations. When properly analyzed, signals from pressure sensors and accelerometers can be useful in detecting the occurrence and intensity of engine knock.
Various techniques are known to those skilled in the art for analyzing signals received from pressure sensors and accelerometers for the purpose of detecting the occurrence of engine knock. In addition, various mathematical and statistical techniques are known by those skilled in the art for processing a stream of sequential signals received from either a pressure sensor or an accelerometer.
U.S. Pat. No. 6,330,874, which issued to CIANCIARA et al on Dec. 18, 2001, describes a method for cylinder-selective knock control of an internal combustion engine. The total ignition angle of each cylinder is composed of cylinder-selective values basic ignition angle, knock adjustment angle, in addition to a first adaptation value and a second adaptation value which are common to all cylinders. The first adaptation value is increased when the knock adjustment angle is greater than a threshold magnitude and is reduced when the knock adjustment angle is less than a threshold. The second adaptation value is formed as a function of the average value of the adaptation values for all cylinders.
U.S. Pat. No. 5,744,698, which issued to Genot on Apr. 28, 1998, describes an accelerometric sensor for measuring the piston knock of an internal combustion engine. The sensor is intended for measuring pinging in an internal combustion engine. The sensor includes a base in the form of a sleeve with a flange extending therefrom and supporting at least one stacked piezoelectric ring, connecting disks and a seismic weight. The underside of the base is used as a contact surface between the sensor and the part to be measured. The underside has a central recess such that the average load distribution diameter over the contact surface is no smaller than the average of the shoulder. This shape may be achieved with a recess which is coaxial with the sleeve and which has a diameter greater than the external diameter thereof. The shape may alternatively be achieved by forming the underside in a concave shape.
U.S. Pat. No. 5,645,034, which issued Entenmann et al on Jul. 8, 1997, describes a method for the adaptive knock control of an internal combustion engine. The method serves the purpose of shifting the ignition angle of an internal combustion engine in the retard direction when knocking occurs and for subsequently carrying out a return of the ignition angle in the advance direction. At the same time, the internal combustion engine is to have sub-divided operating ranges, and a value of an ignition-angle retard, determined in a range during operation, is always stored when this range is left. At the same time, in particular an average of all the ignition angles outputted in a range or a retard value is plotted by a digital low-pass filter and is stored.
U.S. Pat. No. 5,140,962, which issued to Iwata on Aug. 25, 1992, describes a knock sensing apparatus for an internal combustion engine. The apparatus is intended for use with a multi-cylinder internal combustion engine and has a knock sensor that generates an electrical output signal corresponding to vibrations of the engine. A peak hold circuit generates a level signal indicating the level of the output signal of the knock sensor during a prescribed period. The level signal is compared with a threshold determined by the operating region of the engine. When the level signal exceeds the threshold level, it is determined that the engine is knocking. According to one form of the present invention, the threshold is determined on the basis of the output signals from a plurality of sensors for sensing different operating conditions of the engine. In a preferred embodiment, the sensors include a sensor for sensing an indication of the engine rotational speed and an engine load sensor. According to another form of the present invention, the threshold is then corrected in accordance with the difference between the actual noise level of the engine as indicated by an average of the level signal and an expected noise level determined by the operating condition detected by the sensor. The corrected threshold is then compared with the level signal to determine if knocking is taking place.
U.S. Pat. No. 5,083,278, which issued to Matsuura on Jan. 21, 1992, describes a knocking detection device for an internal combustion engine. An improvement of a knocking detection device is disclosed for an automotive engine mounted on a vehicle having a knock sensor for detecting analog vibration waveforms of the engine, and a crank position sensor for producing signal corresponding to a predetermined crank angle of the engine. The devise comprises a conversion circuit for converting the analog waveforms detected by the knock sensor into digital data every predetermined sampling period; a decision circuit for deciding a first conversion term corresponding to no knocking period and a second conversion term corresponding to knocking possibility period in one cycle of the engine; a setting circuit for setting a discrimination level based on a first average value of the digital data from the conversion circuit during the first conversion term decided by the decision circuit; calculation circuit for calculating knocking level based on a second average value of the digital data for the conversion circuit during the second conversion term decided by the decision circuit; and a determination circuit for determining knocking occurrence by comparing the knocking level calculated by the calculation circuit with the discrimination level set by the setting circuit, so as to determine knocking occurrence when the knocking value is larger than the discrimination level.
U.S. Pat. No. 5,060,615, which issued to Hashimoto et al on Oct. 29, 1991, describes a knock sensing apparatus for an internal combustion engine. The apparatus has a knock sensor that generates an electrical output signal corresponding to vibration of the engine. A level indicating means generates a first level signal indicating the level of the output signal of the knock sensor during the first period at least partially coinciding with the power stroke in a cylinder of the engine and a second level signal indicating the level of the output signal of the knock sensor during a second period. An averager forms an average of the second level signal over a prescribed period, and a threshold calculator calculates a threshold based on the average. A comparator compares the first level signal and the threshold and generates a signal indicating knocking when the first level signal exceeds the threshold.
U.S. Pat. No. 4,971,007, which issued to Gopp et al on Nov. 20, 1990, describes a system and method for combined knock and torque timing control. The system control ignition knock while maintaining minimum spark for best torque. Both knock control and minimum spark for best torque control are simultaneously utilized. During knock control, engine cycles are counted between successive knock detections. When the count is less than a first value, a retard signal is generated. An advance signal is generated when the count is greater than a second predetermined value. These retard and advance signals are accumulated as knock trim signals in RAM storage locations as a function of engine speed and load operating points for each cylinder. During MBT control, MBT trim signals are generated by determining convergence of an average difference in indicated mean effective pressure for each cylinder. These MBT, or minimum spark for best torque, trim signals are stored in another RAM as a function of speed and load operating points. Base ignition timing is then corrected by both the knock trim signal and corresponding MBT trim signal at each speed and load operating point.
U.S. Pat. No. 4,770,144, which issued to Sakakibara et al on Sep. 13, 1988, describes a knock control apparatus and method for internal combustion engines. The apparatus prevents a variation of a control knock sound even if an output of a knock sensor is varied due to the variations in performance among different engines or knock sensors, aging of the engine or knock sensor or the like. A given correction quantity is added to an average value of an output signal of the knock sensor, and the increased by K times by a K-value varying with the operating conditions of the engine, thereby generating a knock discrimination level. In accordance with the presence of knocking determined by comparing the knock discrimination level and an output signal of the knock sensor, a knock control factor, (e.g. ignition timing, supercharge pressure, or the like) of the engine is controlled.
U.S. Pat. No. 4,111,035, which issued West et al on Sep. 5, 1978, describes an engine knock signal generating apparatus with noise channel inhibiting feedback. A vibration sensor is mounted on an internal combustion engine and is characterized by knock-induced vibrations at a characteristic frequency and by other vibrations. The sensor is tuned to resonate at substantially the characteristic frequency. A band pass filter is tuned to the characteristic frequency and is connected to the vibrations sensor output. The output of the filter is provided to one input of a comparator and to average detector circuitry for generating a unidirectional noise reference signal representing noise at the characteristic frequency. The signal is provided to the other input of the comparator. The knock signal, obtained from the output of the comparator and comprising pulses corresponding to knock-induced peaks of amplitude greater than the unidirectional noise reference signal, is fed back through a low-pass filter to the average detector circuitry in sense to oppose increases in the unidirectional noise reference signal during the knock-induced peaks. The connection of the average detector circuitry to the output of the band pass filter provides adaptability for mistuned sensor; the negative feedback to the average detector circuitry reduces the distorting effect, amplified by the band pass filter, of the knock-induced peaks on the unidirectional noise reference signal, which might otherwise distort the out put knock signal.
U.S. Pat. No. 5,263,365, which issued to Muller et al on Nov. 23, 1993, describes a system for detecting misfires in an internal combustion engine. A system for detecting multiple misfires and for allocating misfires to cylinders for detected multiple misfires in multi-cylinder internal combustion engine is so configured that the rough-running values for the individual cylinders are determined. The system then however forms sum terms with these rough-running values and, in turn, forms sums with these sum terms which sums are compared with threshold values. When at least one sum exceeds the corresponding threshold value, then this shows the presence of multiple misfires. As soon as multiple misfires are detected, the rough-running threshold values for allocating misfires to cylinders are reduced. Advantageously, the rough-running values are so modified in advance that their correction terms are influenced as little as possible by misfires. In this way, misfires can also reliably be allocated to individual cylinders when multiple misfires are present.
U.S. Pat. No. 4,903,664, which issued to Shinshi on Feb. 27, 1990, describes a spark ignition timing control system for internal combustion engines with fail safe system for cylinder pressure sensor. A fail safe system for a cylinder pressure sensor is used for a spark ignition timing control system which calculates a physical quantity for combustion energy within the combustion chamber of an engine cylinder of an internal combustion engine and corrects the spark ignition timing on the basis of the physical quantity. The fail safe system sets a running average of a statistical dispersion of the physical quantity to a predetermined greater value when a specific driving condition (i.e. a high engine load and high engine speed condition) is initially determined, and thereafter compares the running average with a predetermined value when the specific driving condition is detected again to detect abnormality of the cylinder pressure sensor.
It is generally known that a sequence of values can be dynamically used to create and maintain a running sum, or total, which can then be used to dynamically calculate a running average. In other words, a running sum or running total is the arithmetic sum of the most recent previous group of values received from a sensor or other source of values. The use of a running sum is well known and the use of a running sum to calculate an average of a preselected number of most recent events is also well known. Using a running sum, or total, to calculate the average of the most recent preselected number of events has certain advantages, such as reducing the amount of scatter or variation in the average because it is averaged over numerous data points. However, the use of a running sum or average has certain inherent disadvantages. As an example, each of the preselected number of data points used in the running sum (e.g. 50, 100, or more) must be stored in computer memory. In addition, when a new value is received from a sensor, that new value must be included with the preselected number of stored values and the oldest one of that preselected number of stored values must be discarded. In some applications, a pointer is used to identify the most recent one of the preselected number of values, and in other cases, a data buffer is shifted upon the receipt of each new value. In addition, the manipulation of the data in the buffer takes time to execute. This time is added to the calculation time to form the average from the running sum and the known number of preselected values used in the calculation.
It would therefore be significantly beneficial if a substitute for the running sum and running average could be dynamically calculated without the need to store a relatively large preselected number of values in computer memory and perform a shifting or indexing operation prior to each execution of the calculations.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.